1. Field of the Invention
This invention relates to a vehicular lamp, and more particularly to a vehicular lamp applicable to a back lamp of a rear combination lamp.
2. Description of the Related Art
Vehicular lamps are configured to xe2x80x9ccontrol, by the diffraction of a lamp element, the direction of projectionxe2x80x9d (hereinafter simply referred to as xe2x80x9ccontrolxe2x80x9d) of light striking to the lamp element directly or indirectly from a light source bulb.
Conventional vehicular lamps fall in one of a type which is configured with a reflector for reflecting light from a light source bulb and adapted to control the reflected light, as illustrated by FIG. 6A, and a type which is adapted to control direct light from a light source bulb, as illustrated by FIG. 6B. In the reflected-light controlling type of FIG. 6A, light L from a light source bulb 10 is reflected in parallel with an optical axis, by a reflector 12 formed on an inside of a lamp housing 11, and the reflected light LRi is controlled by a fisheye lens element or cylindrical lens element 13 provided in a light transmitting portion of a lens 2 for distribution of projected light LRo. On the other hand, in the direct-light controlling type of FIG. 6B, direct LDi from a light source bulb 10 is controlled by a Fresnel lens element 14 provided in a light transmitting portion of a lens 2 for distribution of projected light LDo. It is noted that, in this Specification, like elements are designated by like reference characters, to eliminate redundancy.
To this point, light distribution of vehicular lamp is regulated by a standard of the country or district, for example, FMVSS SAE J593c, or E/ECE/324, E/ECE/TRANS/505 (Rev. 1/Add. 22, Rev. 1/Amend. 2, Apr. 30, 1998), Regulation No. 23 which requires a lamp to have, as shown in FIG. 7, in a prescribed light distribution range LDR on an imaginary screen 20 at a distance of 10 m, a distribution of light with a luminous intensity equivalent to or greater than a specified value (cd) in a round mark at any of designated upward/downard/leftward/rightward angular positions relative to the optical axis.
However, when the vehicular lamp of FIG. 6A is configured, as shown in FIG. 8A, with a lens 15 having a cylindrical lens element 15a for controlling the reflected light LRi as reference light, the direct light LDi from light source bulb 10 is projected outside the light distribution range LDR, resulting in a proportion of available light reduced to 30 to 40%. On the other hand, if the direct light LDi is controlled as reference light, most of projected light Ldo thereof is concentrated and most of projected light LRo of the reflected light LRi is deviated outside the light distribution range LDR, still resulting in a reduced proportion of available light.
Conventional countermeasure was, e.g. the provision of a reflector with an increased reflective surface area or the like, thus constituting a difficulty to make the lamp compact.
It therefore is an object of this invention to provide a vehicular lamp which can provide a required distribution of luminous intensity within a prescribed light distribution range without increasing a reflective surface area or the like, thus allowing for the lamp to be made compact with case.
To achieve the object, according to an aspect of the invention, there is provided a vehicular lamp comprising: a light source bulb; a reflector for reflecting light from the light source bulb; and a lens provided with a light transmitting portion formed with a set of prism elements for reflected light from the reflector and direct light from the light source bulb to strike thereto, the set of prism elements being configured for controlling the reflected light and the direct light to give a distribution of required luminous intensities in a prescribed light distribution range.
According to this aspect of the invention, both reflected light and direct light are available to illuminate a prescribed light distribution range.